This application is the national phase under 35 U.S.C. xc2xa7 371 of PCT International Application No. PCT/DK99/00332 which has an International filing date of Jun. 17, 1999, which designated the United States of America.
The present invention relates to a conveyor for transporting articles of mixed sizes, such as luggage and/or mail. More particularly the invention relates to a conveyor comprising a plurality of interconnected conveyor units, each comprising an article supporting member, such as a tray or a conveyor belt or any other suitable supporting member. The article supporting members of the conveyor units may be used individually for transporting articles, and two or more consecutive conveyor units may in an aligned state form a common article support surface for transporting articles larger than the individual article supporting member.
The present invention further relates to a pair of conveyor units for use in the conveyor.
Conveyors comprising a plurality of interconnected conveyor units, each comprising an article supporting member are generally known. It is further known to allow articles being conveyed by such conveyors to be carried by supporting members belonging to two or more adjacent conveyor units. However, articles carried by supporting members belonging to two or more adjacent conveyor units tend to shift on the surfaces of the supporting members when the conveyor units enter curves in a horizontal plane along the guide track, since a conveyor unit positioned in front of another conveyor unit will enter the curve before the other conveyor unit, resulting in mutual dispositioning of supporting members supporting the same article. The position of the article may shift so much that the performance and/or operation of the conveyor is disturbed. In some cases, the article may shift so much that it leaves one or more of the supporting members supporting the article, and it may even leave all of the supporting members supporting the article. This is in particular a problem if the conveyor units have to enter many curves while conveying the article. This may occur, e.g., when the guide track is very long and/or if the article has to be conveyed along the guide track several times, e.g. when a barcode, e.g. containing information about the destination of the article, needs to be read and the barcode is not very clear, e.g. due to damage and/or due to the barcode being positioned between the article and the surface of the supporting member, for which reason several passages of the barcode reader is required, thus the article has to travel the entire path of the guide track several times.
European patent No. EP 0 540 464 B1 discloses a conveyor comprising a plurality of trucks coupled together to form an endless chain of trucks, each truck having two dishes which are arranged one behind the other in the direction of travel, the two dishes forming a substantially continuous common supporting surface. The two dishes are capable of pivoting individually so as to unload goods being conveyed by the truck. It is thus possible to tip both, only one or none of the dishes at a certain destination station.
When large articles need to be conveyed by a conveyor as described above, the trucks need to be sufficiently long that the articles may be accommodated by the two dishes of a truck. This puts a lower limit to the radius of curvature of the curves of the guide track which may cause the area requirements of the conveyor to increase.
It is an object of the present invention to provide a conveyor for transporting articles of mixed sizes, the conveyor comprising a plurality of article supporting members, each member individually being able to support articles and at least some of the members being able to form a common article supporting surface for larger articles together with one and optionally more than one adjacent members, the members forming a common article supporting surface being substantially aligned in a projection on a horizontal plane so as to prevent articles from shifting their position when the members move at a path that curves in the horizontal plane and the members being supported by individual conveyor units that are mutually pivotally connected so as to allow the interconnected conveyor units to pass curves having a small radius of curvature, thereby reducing the area requirements of the conveyor.
It is a further object of the invention to provide a conveyor wherein the article supporting members forming a common article supporting surface are substantially aligned during all mutual pivotally movements of the conveyor units.
It is a still further object of the invention to provide a conveyor wherein the article supporting members may be shifted between an aligned and a non-aligned state with an adjacent member.
It is a yet still further object of the invention to provide a conveyor wherein a plurality of the article supporting members may be shifted between an aligned and a non-aligned state with both its immediately adjacent article supporting members so as to increase the flexibility of the conveyor regarding transport of large and small articles.
It is a yet still further object of the invention to provide a conveyor wherein more than two consecutive article supporting members may be aligned so as to make the conveyor more flexible regarding variations of the size of the articles that are conveyed.
The present invention provides a conveyor for transporting articles, the conveyor comprising
a stationary guide track having curved track sections,
at least one loading station for loading articles onto article supporting surfaces of the conveyor,
at least one discharge station for receiving articles from article supporting surfaces of the conveyor, and
a plurality of interconnected conveyor units which are mutually pivotally coupled, each conveyor unit comprising
a frame part,
an article supporting member mounted on and supported vertically by the frame part, the article supporting member having an article supporting surface, and
means for discharging articles from said article supporting member at a predetermined discharge station,
at least one of the plurality of conveyor units belonging to a first group of conveyor units, each of the conveyor units belonging to the first group of conveyor units comprising
first means for aligning the conveyor unit with another immediately adjacent conveyor unit belonging to a second group of conveyor units,
each of the conveyor units belonging to the second group of conveyor units comprising
second means for aligning the conveyor unit with another immediately adjacent conveyor unit belonging to the first group of conveyor units,
said first aligning means and said second aligning means being designed so that when a first conveyor unit belonging to the first group of conveyor units and an adjacent second conveyor unit belonging to the second group of conveyor units are aligned with each other by their respective first aligning means and second aligning means, the article supporting member of the first conveyor unit and the article supporting member of the second conveyor unit are substantially aligned in a projection on a horizontal plane so as to form a substantially common article supporting surface during all mutual pivotally movements of said first conveyor unit and said second conveyor unit.
The stationary guide track may be, e.g., a pair of mutually spaced rails adapted for receiving pairs of wheels which may be positioned on the individual conveyor units. It may alternatively be, e.g., a monorail or any other suitable kind of track. The stationary guide track defines the path of the conveyor. It is preferably a closed track, but it may alternatively be open-ended and establishing a conveyor connection between a loading station which is positioned at one end of the guide track and a discharge station which is positioned at the other end of the guide track.
The stationary guide track may comprise curved track sections being curved in a substantially horizontal plane and/or it may comprise curved track sections being curved in a substantially vertical plane. It may alternatively or additionally comprise curved track sections being curved in a plane having a normal vector having a horizontal as well as a vertical component.
The conveyor units may be, e.g., wagons or carts, and each of them may comprise wheels or other suitable means for engaging with the stationary guide track, so that the conveyor units are guided along the guide track. The conveyor units are interconnected, preferably one behind the other so as to form a chain of conveyor units, most preferably forming a closed loop of conveyor units.
The article supporting members may comprise trays or other suitable means being tiltably mounted on the respective frame parts, in which case the article supporting surface of each supporting member is an upper surface of the tray, and in which case the discharging means are means for tilting the tray. The tilting means may comprise, e.g., one or more tilting tracks positioned along the stationary guide track near at least one of the at least one discharge stations, and one or more tilting wheels positioned on the conveyor unit and adapted for engaging with the tilting track, the tilting track(s) and the tilting wheel(s) being positioned in such a way that a tilting wheel may be made to engage with a tilting track when desired, and in such a way that the tray is tilted when one or more tilting wheels engages with one or more tilting tracks. Thus, a tray may be tilted when desired.
The tilt trays may be fitted with a lip extending upwards from at least a part of the edges of the tray so as to prevent or impede the article from sliding off the tray during operation of the conveyor. These lips are preferably present at the ends in a conveying direction of trays that are not to be aligned with the adjacent tray in that direction, so as to prevent the articles from sliding over to the adjacent tray or into the gap between the adjacent trays.
The article supporting members may alternatively or additionally comprise conveyor belts having a conveying directions which is substantially perpendicular to the direction of transportation of the conveyor, in which case the article supporting surface of each supporting member is an upper surface of the conveyor belt, and in which case the discharging means are means for activating the conveyor belt, thereby applying a velocity to the belt in a direction which is substantially perpendicular to the direction of transportation of the conveyor to the article being conveyed. The belt may thus be activated when a certain conveyor unit is passing a certain discharge station, thereby discharging the article being conveyed by the certain conveyor unit at the certain discharge station.
In order to prevent articles or parts of articles, such as straps or flaps, from extending below the articles supporting surface of the article supporting members and thereby possibly causing a stop of the operation of the conveyor and even severe damage to the conveyor, it has been found to be advantageous that one of the article supporting members of two immediately adjacent conveyor units comprises covering means for covering a possible gab between the article supporting members of the two conveyor units, the covering means engages with the other of the two conveyor units so as to cover the gap during mutual pivotally movements of the two conveyor units.
The covering means may be arranged to cover gaps between the article supporting members of all immediately adjacent conveyor units of the conveyor are covered with covering means during mutual pivotally movements of the adjacent conveyor units or only to cover possible gaps between conveyor units that are or may be aligned with each other.
In a more preferred embodiment of the present invention comprise both of the article supporting members of two immediately adjacent conveyor units covering means for covering a possible gab between the article supporting members of the two conveyor units, the covering means engage mutually so as to cover the gap during mutual pivotally movements of the two conveyor units.
At least one of the covering means may comprises a slidable sheet member extending from the article supporting member of the respective conveyor unit in the direction towards the article supporting member of the other adjacent conveyor unit, the slidable sheet member being mounted slidably substantially in a conveying direction of the conveyer and being resiliently biased towards and engaging with said adjacent conveyor unit.
Additionally or alternatively may at least one of the covering means comprises a pivotally sheet member extending from the article supporting member of the respective conveyor unit in the direction towards the article supporting member of the other adjacent conveyor unit, the pivotally sheet member being mounted pivotally about an axis being substantially perpendicular to the article supporting surface. The pivotally sheet member may thus compensate for mutual pivotal movements in the plane of the article supporting surfaces.
The previously mentioned first conveyor unit and second conveyor unit may preferably constitute the two adjacent conveyor units.
In order to prevent or impede parts of articles being conveyed by the conveyor from being wedged during mutual tilting movements of the article supporting members of the conveyor units, the covering means are preferably at their engaging ends, respectively the covering mean and the conveyor units engaging ends, equipped with screen parts extending downwards from said ends and transversely to the conveying direction of the conveyer in the conveying direction of the conveyer.
The engaging ends of the covering means, respectively the engaging ends of the covering mean and the conveyor units, may be subjected to friction during possible tilting of the article supporting members and due to possible mutual displacement transversely to the conveying direction of the conveyor in which cases the mutually engaging surface parts of the conveyor units and/or the covering means may be coated with a friction reducing and/or wear resistant material.
The first and second aligning means may establish a physical connection between the two conveyor units. They may thus comprise, e.g., a rigid rod which is permanently connected to one of the conveyor units or both of the conveyor units.
Alternatively or additionally, the first and second aligning means may comprise, e.g., magnetic and/or electrical means, so that a magnetic and/or electrical connection may be established between the two conveyor units.
The first and second aligning means do not have to form a physical connection between the two conveyor units. Instead the aligning means may have independent drive means such as an electrical motor, the drive means and thereby the alignment being controlled by control means that is either present on the conveyor unit or is in data communication contact with a control unit on a stationary part of the conveyor. In another embodiment according to the present invention, one or both of the two conveyor units may comprise a guiding arm following a track constituting a part of the guide track, the guiding arm being connected to the article supporting member in such a way that the desired aligning of the article supporting members are obtained. In case the conveyor units comprises a power source, as e.g. cross-belt conveyors usually do, the guide arm may comprise a sensor that provides an output from which a control unit may control an electric motor adjusting the position of the article supporting member accordingly.
The first and second aligning means comprise in an alternative embodiment optical detection means for detecting the position of the article supporting member of an adjacent conveyor unit and/or a detectable object indicating said position. The optical detection means are adapted for providing an output from which a control unit may control an electric motor adjusting the position of the article supporting member accordingly.
When a first and a second conveyor unit are aligned with each other, their article supporting surfaces will be aligned in such a way that when the article supporting surfaces are projected onto a substantially horizontal plane they are substantially aligned in that plane during all mutual pivotally movements of the conveyor units, regardless of whether the mutual pivotally movements take place in a substantially horizontal plane, a substantially vertical plane or in a plane having a normal vector having a horizontal as well as a vertical component. Thus, there are no or very little mutual movements of the projections of the two article supporting surfaces on the horizontal plane, whereby a substantially common article supporting surface is formed by the two article supporting surfaces of the conveyor units.
The conveyor further comprises control means for controlling the operation of the conveyor, including loading of articles onto the article supporting members at one or more loading stations arranged along the path of the conveyor, discharge of articles transported by the conveyor at one or more discharge stations arranged along the path of the conveyor and optionally also controlling the shifting between an aligned and a non-aligned state of adjacent article supporting member. The control means may comprise detection means for detecting the presence, the location and/or the size of articles that are conveyed or might be conveyed by the conveyor, it may additionally of alternatively comprise means for reading identification tags associated with the articles, such as e.g. barcode labels, character codes or other optically detectable codes, transponder tags, etc., and it may additionally or alternatively comprise means for reading identification tags associated with the individual conveyor unit and/or article supporting member.
The article supporting member of each conveyor unit may preferably be pivotally connected to the frame part of the conveyor unit about an aligning axis being substantially vertical. When a conveyor unit enters a curve, it may, thus, be possible for the frame to follow the guide track, i.e. to turn, while the article supporting member, or at least the article supporting surface, keeps moving in the tangential direction in which it was moving before the conveyor unit entered the curve. This may be utilised when the article supporting surface of the conveyor unit in question is aligned with the article supporting surface of an adjacent conveyor unit. Since the two conveyor units are positioned one behind the other, one of the conveyor units.will enter a curve along the guide track before the other one does. If the article supporting surfaces are not aligned, this will result in mutual pivotally movements in a substantially horizontal plane of the article supporting surfaces of the two conveyor units. If, however, the article supporting surfaces are aligned, a substantially common article supporting surface may be maintained, even when the conveyor units enter a curve along the guide track, and even if the radius of curvature of the curve is so small that a conveyor unit having an article supporting surface having an area corresponding to the area of the common article supporting surface, is not allowed to enter the curve.
Thus, a conveyor which is capable of carrying articles of different sizes with efficient utilisation of the article supporting area of the conveyor is provided, the conveyor being less area consuming than conventional conveyors, since the curves of the conveyor may have a smaller radius of curvature than conventional conveyors being capable of carrying large articles.
Preferably, the stationary guide track forms a closed loop, so that the individual conveyor units may complete a loop routine including receiving an article at a loading station, carrying the article to a certain discharge station, discharging the article at the discharge station and returning to the loading station without having to reverse the direction of motion.
Most preferably, the plurality of conveyor units form a closed chain of conveyor units. Thus, there is preferably a closed chain of conveyor units fully covering a closed loop formed by the stationary guide track.
At least one of the at least one discharge stations may have means associated with it for activating the discharge means of at least two consecutive conveyor units in such a way that the discharge means of the at least two consecutive conveyor units are activated with a predetermined time interval so as to enable discharge of an article being supported by more than one of the supporting members of the at least two consecutive conveyor units at the discharge station.
The activating means may be mechanical. In an embodiment in which the article supporting members comprise one or more trays, the mechanical activating means may comprise, e.g., one or more tilting tracks positioned along the stationary guide track near the discharge stations, and adapted for engaging with wheels positioned on the individual conveyor unit, the tilting track(s) and the tilting wheel(s) being positioned in such a way that a tilting wheel may be made to engage with a tilting track when desired, and in such a way that the tray is tilted when one or more tilting wheels engages with one or more tilting tracks.
Alternatively or additionally, the activating means may be electrical and/or magnetic and/or pneumatic and/or hydraulic and/or any other suitable kind of activating means.
Preferably, the supporting surfaces of the at least two consecutive conveyor units are aligned by first and second aligning means. Thus, an article being carried by the two or. more consecutive conveyor units may be discharged at a certain discharge station by activating the discharge means of all the conveyor units carrying the article.
The discharge means of all the consecutive conveyor units may be activated at the same time, so as to discharge the article instantly. They may alternatively be activated with a predetermined time interval which is greater than zero in such a way that the discharge means of the conveyor unit being in front is activated before the discharge means of the lacking conveyor unit. Thus, a transverse velocity will be applied to the front end of the article as compared to the lacking end, whereby the article is turned, substantially around the middle of the article. In case the dimensions of the article are so that the article stretches in one direction, it is often desired that this direction substantially coincides with the direction of transportation. It may thus be desired that the article is turned when the direction of transportation changes, e.g. when the article is discharged.
The first aligning means may comprise a rigid aligning member and the second aligning means may be designed for engaging with the rigid aligning member of a first aligning means. The first aligning means and the second aligning means may be designed so as to allow for variations in the distance between the positions at which the first aligning means and the second aligning means of immediately adjacent conveyor units connect with the respective conveyor units, the immediately adjacent conveyor units being aligned by the first aligning means and the second aligning means.
The rigid member may be, e.g., a rod being connected to the conveyor units belonging to the first group of conveyor units and the second aligning means may comprise, e.g., a hollow part adapted for receiving the rod. It may comprise locking means, such as grooves and protrusions adapted for engaging with each other and/or fastening means such as screws, for permanently or non-permanently locking the first aligning means and the second aligning means together.
Preferably, the first aligning means and the second aligning means are designed so as to allow for variations in the distance between the positions at which the aligning means connect to the respective conveyor unit. When two consecutive conveyor units enter a curve of the guide track and the supporting surfaces of the two conveyor units are aligned, it may be necessary to alter the distance between the above mentioned positions in order to keep the supporting surfaces aligned while the frame members of the conveyor units perform mutual pivotally movements. The distance may need to be increased or decreased depending on in which direction the guide track is curved as compared to the position of the first and second of the respective conveyor units.
Alternatively or additionally the first and the second aligning means comprise an independent drive means for driving a mechanism for pivoting the article supporting member about at least one aligning axis being substantially perpendicular to the article supporting surface.
The independent drive means may be e.g., a electrical motor, a pneumatic motor or a hydraulic motor.
The mechanism for pivoting the member may comprise e.g.,
at least two wheels e.g. pinion wheels or friction wheels, which are able to transmit an angular moment from one wheel to the other, or
a wheels-and-rim mechanism e.g., a notched wheels and notched rim, V-belt wheels and V-belt, sprocket wheels and chain, a rack and pinion drive or a non-linear rack and pinion drive.
This type of aligning mechanism is mainly used when the conveyor unit has an onboard power supply which generally is the case when an electrical tilting mechanism or a cross-belt is employed, but further the conveyor could use a pneumatic or hydraulic motor if there for some reason is pressurised air or hydraulic pressure present on the conveyor unit.
In embodiments wherein each of the conveyor units belonging to at least one of the first group and the second group of conveyor units comprises a tray, the tray may be arranged tiltably about a tilt axis. The tilt axis may be substantially parallel to the direction of transportation of the conveyor, the tilt axis of a first conveyor unit belonging to the first group of conveyor units being substantially coincident with the tilt axis of an adjacent second conveyor unit belonging to the second group of conveyor units, the first conveyor unit and the second conveyor unit being aligned with each other by their respective first aligning means and second aligning means, when the first conveyor unit and the second conveyor unit are placed on a substantially straight part of a guide track.
When the conveyor units are moved on a substantially straight part of a guide track both of the aligned trays may, thus, be tilted about substantially coincident tilt axes, whereby an article being supported by both article supporting surfaces may be discharged by tilting the two trays at the same time or with a predetermined time interval. When the conveyor units enter a curve along the guide track and the respective article supporting surfaces are aligned with each other, the tilt axes will still be substantially coincident with each other, thus allowing an article being supported by both article supporting surfaces to be discharged when being conveyed during a curve of the guide track.
The first aligning means and the second aligning means may further be designed in a way that allows for pivotal movements between the positions at which the first aligning means and the second aligning means of immediately adjacent conveyor units connect with the respective conveyor units. The pivotal movements are preferably allowed about an axis that substantially coincide with the tilt axes of the conveyor units being aligned by the first and the second aligning means so as to enable individual tilting movements of the trays of the conveyor units.
It is, thus, preferably possible to tilt both of the aligned trays, only one of the trays or none of the trays when the conveyor units pass a discharge station, so that consecutive trays may be utilised for carrying large articles occupying two or more trays, or for carrying small articles occupying only one tray, thus providing a conveyor which is very flexible, the capacity of which is exploited in an efficient way.
The first aligning means and the second aligning means may additionally be connected with the respective conveyor units in a way that allows for pivotal movements between the individual aligning means and the respective conveyor unit about an axis being substantially horizontal and substantially perpendicular to the direction of transportation of the conveyor so as to allow for conveyor units being aligned by first aligning means and second aligning means to move along guide track sections curved in projection on a vertical plane.
Thus, the aligning means may allow for pivotal movements between the individual aligning means and the respective conveyor units about two substantially perpendicular axes, thus effectively allowing for pivotal movements in any direction. This may be obtained by providing the aligning means with two pivot axes being substantially perpendicular to each other. It may alternatively be obtained by mounting the aligning means on the respective conveyor units by a sphere or part of a sphere, thus allowing the aligning means to pivot in any direction as compared to the respective conveyor unit.
The article supporting member of each conveyor unit may be pivotally connected to the frame part of the conveyor unit about an axis being substantially horizontal, substantially perpendicular to the direction of transportation of the conveyor, and substantially intersecting the vertical axis about which the article supporting member is pivotally connected to the frame part so as to enable that the article supporting member of the first conveyor unit belonging to the first group of conveyor units and the article supporting member of the second conveyor unit belonging to the second group of conveyor units, said first and second conveyor units being aligned by the first and second aligning means, may be substantially aligned so as to form a substantially common article supporting surface during all mutual pivotally movements of said first conveyor unit and said second conveyor unit.
As described above, this may be obtained by providing the article supporting member with two pivot axes being substantially perpendicular to each other, or it may alternatively be obtained by mounting the article supporting member on the frame part using a sphere.
In this embodiment it is possible to align consecutive article supporting members during all mutual pivotal movements of the conveyor units, such as when the conveyor units enter curves along the guide track which are curved in a substantially horizontal plane or in a substantially vertical plane or in any other suitable plane in which the guide track may be curved.
The first aligning means and the second aligning means may further be designed so that the article supporting member of the first conveyor unit and the article supporting member of the second conveyor unit, said first and second conveyor units being aligned by the first and second aligning means, are substantially aligned so as to form a substantially common article supporting surface during all mutual pivotally movements of said first conveyor unit and said second conveyor unit.
In one embodiment of the invention the first and the second aligning means may connect the trays of the conveyor units being aligned by the first and the second aligning means. This may be obtained, e.g., by applying one or more rods, preferably two rods, to the respective trays.
The alignments established by the first and second aligning means may be permanent Thus, a permanent physical connection may be applied when the conveyor is installed, so that the conveyor units are connected two by two, three by three or even higher numbers.
In a preferred embodiment, all of the conveyor units belong to the first group of conveyor units as well as to the second group of conveyor units. Thus, all of the conveyor units preferably comprise first aligning means as well as second aligning means, so that any conveyor unit is capable of aligning its article supporting surface with the article supporting surface of any other adjacent conveyor unit.
Most preferably, the first aligning means and the second aligning means are designed for having a first state in which alignment is established between the article supporting members of the first and the second conveyor units, and a second state in which alignment is not established, and the conveyor comprises means for switching between said first state and said second state.
Any conveyor unit may be capable of aligning with both of the conveyor units being immediately adjacent by means of the first and second aligning means when desired.
In an embodiment in which all of the conveyor units belong to the first as well as the second group of conveyor units, and in which the second aligning means are designed for having a first state in which alignment is established between the article supporting members of the first and the second conveyor units, and a second state in which alignment is not established, and the conveyor comprises means for switching between said first state and said second state, alignment between supporting members of any adjacent conveyor units may be obtained when desired. Thus, an extremely flexible conveyor is provided, in which alignment of the required number of article supporting surfaces may be provided whenever it is needed, so that articles of different sizes may be conveyed by the conveyor in any order, and so that the capacity of the conveyor is exploited in the most efficient manner possible.
Thus, a very flexible conveyor having a large capacity is provided.
In another aspect of the present invention is provided a pair of conveyor units for use in a conveyor as described above, wherein the first conveyor unit is adjacent to the second conveyor unit and each of the conveyor units comprising
a frame part,
an article supporting member mounted on the frame part, the article supporting member having an article supporting surface, and
means for discharging articles from said article supporting member at a predetermined discharge station of the conveyor,
the first conveyor unit comprising
first means for aligning the first conveyor unit with the second conveyor unit,
the second conveyor unit comprising
second means for aligning the second conveyor unit with the first conveyor unit,
said first aligning means and said second aligning means being designed so that when the first conveyor unit and the second conveyor unit are aligned with each other by their respective first aligning means and second aligning means, the article supporting member of the first conveyor unit and the article supporting member of the second conveyor unit are substantially aligned in a projection on a horizontal plane so as to form a substantially common article supporting surface during all mutual pivotally movements of said first conveyor unit and said second conveyor unit.
The article supporting surfaces of the conveyor units of the conveyor may be aligned two by two.
Three or more article surfaces may be aligned in such a way that one or more of the three or more article supporting surfaces is aligned with the article supporting surfaces of both of the adjacent conveyor units.
Further scope of the applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications-within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.